When a person has so many illnesses and diseases trying to kill them, that they cancel each other out - much like when all three of the Three Stooges are attempting to get through a doorway at the same time and get stuck as a result. Coined on 'The Simpsons' in reference to Mr Burns' health. Mr. Burns interpreted this condition as indestructibility.

'The only reason that guy can possibly still be alive is if he has Three Stooges Syndrome.'